Some labs-on-a-chip can perform experiments on single atoms or ions, but it’s only recently that researchers have figured out how to corral molecules onto a chip surface. A German research team has now made an important step in the development of molecule-on-a-chip technology with the demonstration of on-chip molecular detection. As described in Physical Review Letters, the technique, which involves ionizing molecules trapped on a 80-millimeter-long chip, can provide time-resolved spatial imaging of small molecular clouds.

Chips that manipulate cooled atoms or ions have performed a variety of tasks, such as quantum computations and gravitational sensing. Molecule chips, by contrast, have lagged behind, in part because molecules have a much richer, more complicated excitation spectrum that makes it difficult to cool and control them.

In recent work, the research group at the Fritz Haber Institute of the Max Planck Society, Germany, has developed methods for trapping and manipulating molecules on a chip. Now, Silvio Marx and his colleagues have added a new tool to their repertoire, with the first on-chip molecular detector. The team first loads a molecule chip with carbon monoxide (CO) molecules that have been cooled through supersonic expansion. Gold microelectrodes on the chip produce tiny traps, which each hold a cloud of about five CO molecules. A varying voltage on the electrodes moves the traps, so that the molecules can be smoothly decelerated and delivered to a laser beam that “snaps a picture” of the molecules by ionizing them. The resulting ion cloud is magnified by a system of ion lenses and imaged on a phosphor screen several centimeters above the chip. Compared to off-chip detection schemes, this method allows for the direct measurement of the spatial distribution of molecules and can capture short-lived quantum states. – Michael Schirber

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